NMAC WITH SMT WHILE ON VISUAL APCH LGB.

Narrative

I HAD CONTACTED LGB TWR APPROX 10 MI EAST AND RECEIVED INSTRUCTIONS TO RPT THE 605 FREEWAY E OF THE ARPT AT OR ABOVE 2000'. FLYING ON A HDG OF 250 DEGS; LINED UP WITH RWY 25L; I HAD XED LOS ALAMITOS ARPT AT 3000' TO AVOID THEIR ATA AND HAD JUST THROTTLED BACK TO REDUCE SPD FROM 150 MPH TO 100 MPH TO BEGIN DSCNT AND LOWER LNDG GEAR (GEAR DOWN SPD IS 100 MPH). AT APPROX 2700' IN MY DSCNT I WAS STARTLED TO SEE A TWIN CROSS FROM MY LEFT TO RIGHT APPROX 300' IN FRONT OF ME AT THE SAME ALT. IT APPEARED THAT HE WAS CLBING AT THIS TIME. I OBSERVED THE ACFT FLY N-ERLY UNTIL APPROX 5 MI N OF LGB; AND THEN TURN WBOUND. BY THIS TIME I HAD XED THE 605 FREEWAY AND RECEIVED CLRNC TO LAND BY THE LGB TWR. THE TWR AT NO TIME SEEMED TO BE AWARE OF THE ACFT IN THEIR ATA. DUE TO RADIO CONGESTION; I DID NOT ADVISE THE TWR OF THE CONFLICT. I DO NOT FEEL THE OTHER ACFT WAS EVER AWARE OF MY ACFT. IT WAS NOT A LIFE OR DEATH MATTER. MY ATTN WAS DIRECTED TOWARDS THE LNDG APCH AND SCAN HAD BEEN LIMITED TO THIS AREA.